1. Field of the Invention
The present invention relates to an image forming method and an image forming apparatus, and specially relates to an image forming method and an image forming apparatus, which can be applied for a printer or a photocopier using a two-component developer.
2. Description of the Related Art
According to an electrophotographic or electrostatic recording image forming method, a latent electrostatic image is formed on a latent electrostatic image bearing member such as a photoconductive material, the latent electrostatic image is developed by depositing a charged toner onto the latent electrostatic image to form a visible image (a toner image), the visible image is transferred to a recording medium, and the transferred visible image is fixed to thereby form an output image. After completing the developing operation of the developing step, the developer from which the toner has been consumed is collected, and then mixed and/or stirred with a supply toner to thereby return to a developing step.
The developer used for the aforementioned image forming method needs to maintain a constant toner density and charged amount to stably provide a toner image.
The toner density is adjusted with an amount of the toner supplied to compensate the toner consumed in the developing step. Moreover, the charge is adjusted with frictions, as it is applied by frictional electrification when the carrier and the toner are mixed.
Accordingly, the two-component developer consisting of the toner and the carrier is sufficiently stirred in the developing step, to equalize the toner density distribution, and to charge the toner, to thereby stabilize the toner image.
As illustrated in FIG. 10, in the conventional image forming method, dispersion and application of charge to the toner is performed by utilizing the stirring effect from the rotations of two screws 163, 164 in the developing element 150 during only a short period from the time when the toner enters into the developing element for supplying to the supplied toner is scoped and born on the developing sleeve. When the amount of the toner supplied is large to compensate the consumed toner, the supplied toner is scoped onto the developing sleeve without being sufficiently dispersed, which may cause problems in qualities of the resulting images, because of back ground deposition, and toner scattering.
To solve this problem, there is a method for enhancing the stirring by the rotations of the two screws.
When the stirring is enhanced, however, the stress applied to the developer increases, which may cause toner spent on the carrier after using a long period of time, and cracking of the carrier coat film (carrier coat layer), lowering the charge imparting ability.
There is disclosed a method for maintaining a constant toner density and charged amount without providing large stress to a developer, when a large amount of a toner is supplied to the developer, where the method uses a developing device, in which a stirring unit is separately provided outside a developing element, the developing element and the stirring unit are connected with a developer circulating unit, the stirring unit is configured to perform stirring depending on the condition of the developer with low stress, and the developer whose toner density and charged amount are appropriately adjusted is supplied to the developing element (see Japanese Patent (JP-B) No. 3734096, and Japanese Patent Application Laid-Open (JP-A) No. 2008-299217). In this method, the developer prepared (optimized) by the stirring unit is transferred (transported) to the developing element by air pressure while regulating the discharging amount of the developer with a rotary feeder.
In this method, however, air leakage through the developer increases when the developer has high flowability and a sufficient amount of the developer transferred cannot be secured, as the developer is transferred through the pipe by air pressure. Accordingly, there are variations in the amount of the developer transferred. To stably provide toner images, a constant amount of the developer needs to be continuously and effectively transferred to the developing element.
Accordingly, it is currently strongly desired to provide an image forming method, and image forming apparatus, by which a developer of a constant density, in which a toner and a carrier are uniformly mixed, can be prepared, an appropriate charge amount can be efficiently provided without providing stress to the developer, and a constant amount of the developer can be continuously, stably and effectively transported to a developing element.
The present invention aims to solve the aforementioned various problems in the art and to achieve the following object. An object of the present invention is to provide an image forming method and image forming apparatus, by which a developer of a constant density, in which a toner and a carrier are uniformly mixed, can be prepared, an appropriate charge amount can be efficiently provided without providing stress to the developer, and a constant amount of the developer can be continuously, stably and effectively transported to a developing element.